Endothelial changes in saphenous veins harvested for coronary artery bypass grafts were found when veins prepared in this manner were examined using the scanning and transmission electron microscopes. Using current distention pressures and preservation techniques, severe endothelial disruption was found. We compared the endothelial changes caused by a variety of currently employed vein handling techniques to determine the best method to protect venous endothelium during the bypass procedure.